Uniforms and clothing for the CCC were provided by the US Army's Quartermaster Corps (QMC).
In the 1930s the QMC was a vast industrial enterprise. Regional Quartermaster Depots (QMDs) located throughout the country supplied shoes, uniforms and equipment to Army posts and garrisons in their service areas. Certain of these Depots were more than just distribution warehouses--they also included design studios, contract and procurement offices, and vast workshops. Among the most significant of these major depots were Philadelphia, which specialized in the design, manufacture and procurement of clothing and textiles; Boston, which specialized in shoes and footwear (New England was the historic center of the US shoe industry); and Jeffersonville, Indiana, which specialized in leather belts, canvas packs, and web gear.
Some Army equipment was made in-house: for example, clothing at Philadelphia QMD, shoes at Boston, and web belts and canvas canteen covers at Jeffersonville. More commonly, uniform items were manufactured by civilian firms under contract. Each such garment had sewn into it a tag in a standardized format identifying the contract under which it was produced, and the specification -- i.e., the approved design or pattern -- to which it should adhere. Contract codes began with a W (War Department), followed by a number code for the supervising Quartermaster Depot (usually 669, i.e., Philadelphia QMD for textiles), followed by a contract number in lineal sequence.
These contract codes are of vital importance for identifying Civilian Conservation Corps garments. Each contract for CCC clothing was identified in the contract code as a CCC procurement rather than general Army contract. To identify the CCC contracts, the Quartermaster Corps inserted the letters ECF (Emergency Conservation Fund), ECW (Emergency Conservation Work), or CIV (Civilian), into the contract code before the lineal contract number. The first two abbreviations were used until about 1936; after a period of transition, CIV became the common code from 1938 onward.
The Quartermaster Corps would spend its own money to execute the contracts, and at the end of the fiscal year, QM accountants would total up the value of the CCC contracts and bill the Treasury Department for reimbursement. The Treasury would repay the War Department out of the CCC Treasury Department account.
To cut to the chase:
Quartermaster Corps garment tags containing the letters ECF, ECW, or CIV in the contract number definitively identify a garment as having been bought with CCC funds. By extension, they also identify a clothing specification approved for CCC issue.
Specification codes were organized by material. Cotton goods were in class 6, silk in class 7, wool in class 8, and leather in class 9. So, a pair of khaki cotton trousers might conform to Specification 6-254 -- the 254th specification in the cotton goods class. Minor changes to the specification would be noted by appending a letter to the code; so, Specification 8-83B would be the second version of Specification 8-83 for wool trousers.
For garments which were specific to the CCC and not intended for issue to the Army, the Quartermaster usually published only a dated Tentative Specification. Such procurements were deemed to be short-term or experimental, and not worth recording with a standing specification number.
Here is a sample tag for a World War II-era Army procurement, in this case from a pair of trousers:
The Contract Number is W-669-qm-22392 executed on October 26, 1942.
The Specification for this type of trouser is 6-254 adopted on November 8, 1937.
And here is a similar tag for a cold-weather hat procured for the CCC:
The Contract Number is W-669 QM-CIV-548 executed on June 24, 1941.
The Specification for this type of cap is 6-255A adopted October 15, 1940.